Substrate with transparent electrode and method for manufacturing same

ABSTRACT

A substrate with a transparent electrode which includes an amorphous transparent electrode layer on a transparent film substrate. When a bias voltage of 0.1 V is applied to the amorphous transparent electrode layer, the layer has continuous regions where a current value at a voltage-applied surface is 50 nA or more. Each of the continuous regions has an area of 100 nm2 or more and the number of the continuous regions is 50/μm2 or more. In one embodiment, the layer has a tin oxide content of 6.5% or more and 8% or less by mass. With respect to the substrate with a transparent electrode according to the present invention, the transparent electrode layer may be crystallized in a short period of time.

CROSS REFERENCE TO RELAYED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/653,805 (now U.S. Pat. No. 9,903,015), entitled SUBSTRATE WITHTRANSPARENT ELECTRODE AND METHOD FOR MANUFACTURING SAME, filed Jun. 18,2015, which is the U.S. National Phase of International PatentApplication No. PCT/JP2013/083905, entitled SUBSTRATE WITH TRANSPARENTELECTRODE AND METHOD FOR PRODUCING SAME, filed Dec. 18, 2013, which inturn claims priority to Japanese Patent Application No. 2012-277453,filed Dec. 19, 2012. Each of these applications is hereby incorporatedby reference in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates to a substrate with a transparentelectrode in which a transparent electrode layer is provided on atransparent film substrate. Particularly, the present invention relatesto a substrate with a transparent electrode layer for a capacitive touchpanel, and a method for manufacturing the substrate with a transparentelectrode layer.

BACKGROUND ART

A substrate with a transparent electrode, in which a transparentelectrode layer composed of a conductive oxide thin film is formed on atransparent substrate such as a transparent film or glass, is widelyused as a transparent electrode of a display, a touch panel, or thelike. Principal factors that determine performance of a substrate with atransparent electrode include an electric resistance and a lighttransmittance of a transparent electrode layer, and an indium-tincomposite oxide (ITO) is widely used as a material having both a lowresistance and a high transmittance.

In recent years, a substrate with a transparent electrode, whichincludes a transparent electroconductive layer having a lower resistancethan those in the past, has been needed as the size of screens ofdisplays and touch panels have increased. Patent Document 1 describesthat when the tin oxide content of ITO on a glass substrate isincreased, the carrier density increases, so that an ITO transparentelectrode layer has a reduced resistance. More specifically, in PatentDocument 1, film formation is performed at a substrate temperature in arange of 230 to 250° C. using a target with a tin oxide content of about10% by mass.

On the other hand, when a film is used as a transparent substrate, thesubstrate temperature cannot be raised during film formation in view ofthe heat resistance of the substrate. Therefore, when a film substrateis used, a method is widely used in which an amorphous ITO film isformed on a film substrate by a sputtering method at a low temperature(e.g. 150° C. or lower), and then heated/annealed under an oxygenatmosphere to transform the amorphous ITO film into a crystalline ITOfilm. However, there is the problem that as the tin oxide content of theITO film becomes greater, an amount of time required for crystallizationincreases, and therefore productivity of a substrate with a transparentelectrode is reduced, or crystallization is insufficient, so that areduction of the resistance is hindered as described in Patent Document2.

When an ITO film is formed on a glass substrate as a measure against theabove-mentioned problem, the time required for crystallization can bereduced by annealing the ITO film at a high temperature of 200° C. orhigher. However, since a film substrate cannot withstand such a hightemperature, an ITO film formed on a transparent film substrate shouldbe crystallized at a relatively low temperature of about 150° C., andthus it is not easy to improve productivity by reducing the timerequired for crystallization.

Patent Document 3 describes a method in which ITO having a high tinoxide content and ITO having a low tin oxide content are laminated toreduce the time required for crystallization. In the method in PatentDocument 3, however, a sufficient reduction of the resistance of the ITOfilm after crystallization is hindered because ITO having a low tinoxide content is partially used. For laminating a plurality of ITO filmshaving different tin oxide contents, a plurality of targets havingdifferent tin oxide contents should be used, which may cause a reductionin productivity and an increase in cost of production equipment.

Patent Document 4 describes that when the water partial pressure in achamber before the start of formation of an ITO film and duringformation of the ITO film is extremely reduced to 1.0×10⁻⁴ Pa or less,the time required for crystallization of the ITO film can be reduced. Toachieve such a low partial pressure, moisture and gases adsorbed to asubstrate film should be removed by reducing the chamber pressure beforethe start of formation of an ITO film. When the inside of the chamber isevacuated using a vacuum pump, the time required for evacuationexponentially increases as the ultimate pressure becomes lower (theultimate vacuum degree becomes higher). For reducing the water partialpressure in a chamber to 1.0×10⁻⁴ Pa or less before the start offormation of an ITO film, a long period of time is needed for evacuationbefore film formation, so that the time required to complete filmformation after introduction of a film substrate into the chamber(occupancy time of film deposition apparatus) increases, and thereforeproductivity as a whole tends to be reduced, although thecrystallization time is reduced.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP-A-2011-18623

Patent Document 2: JP-A-2010-80290

Patent Document 3: JP-A-2012-114070

Patent Document 4: JP-A-2012-134085

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In view of the above-mentioned problems, an object of the presentinvention is to provide a substrate with a transparent electrode whichis excellent in productivity and which includes a low-resistance ITOfilm. More specifically, an object of the present invention is toprovide a substrate with a transparent electrode in which an amorphoustransparent electrode layer capable of being crystallized in a shortperiod of time by annealing at a relatively low temperature is providedon a transparent film substrate with the use of an ITO target having ahigh tin oxide content.

Means for Solving the Problems

The present inventors have conducted intensive studies, and have foundas a result that when the amount of low-resistance grains in anamorphous transparent electrode layer before crystallization isincreased, activation energy required for crystallization can bedecreased, so that the time required for crystallization can be reduced.

That is, the present invention relates to a substrate with a transparentelectrode in which an amorphous transparent electrode layer is providedon a transparent film substrate, and the amorphous transparent electrodelayer contains an amorphous indium-tin composite oxide having a tinoxide content of 6.5% by mass or more and less than 16% by mass. When abias voltage of 0.1 V is applied to the amorphous transparent electrodelayer, the amorphous transparent electrode layer has continuous regionswhere a current value at a voltage-applied surface is 50 nA or more.Each of the continuous regions has an area of 100 nm² or more. Thenumber of the continuous regions is 50/μm² or more.

In one embodiment of the substrate with a transparent electrodeaccording to the present invention, the tin oxide content of theamorphous transparent electrode layer is more than 8% by mass and lessthan 16% by mass. When the content of tin oxide falls within theabove-mentioned range, a crystalline transparent electrode layer havinga lower resistance is obtained in crystallization of the amorphoustransparent electrode layer by heating. In another embodiment of thesubstrate with a transparent electrode according to the presentinvention, the tin oxide content of the amorphous transparent electrodelayer is 6.5% by mass to 8% by mass. When the content of tin oxide fallswithin the above-mentioned range, a low resistivity can be maintained,and the time required for crystallization can be further reduced.

A thickness of the amorphous transparent electrode layer is preferably10 nm to 35 nm. The time required for crystallization of the amorphoustransparent electrode layer is preferably 30 minutes or less when theamorphous transparent electrode layer is heated at 150° C. Activationenergy for crystallization of the amorphous transparent electrode layeris preferably 1.3 eV or less. A resistivity after the amorphoustransparent electrode layer is subjected to a heating treatment at 150°C. for 30 minutes is preferably 1.5×10⁻⁴ to 3.0×10⁻⁴ Ωcm.

Further, the present invention relates to a method for manufacturing asubstrate with a transparent electrode in which an amorphous transparentelectrode layer is provided on a transparent film substrate, and thetransparent film substrate contains ITO having a tin oxide content of6.5% by mass or more and less than 16% by mass. In the manufacturingmethod of the present invention, a transparent electrode layercontaining an amorphous indium-tin composite oxide is formed on atransparent film substrate using a sputtering method (transparentelectrode layer forming step). In the transparent electrode layerforming step, a composite oxide target of indium oxide and tin oxide,which has a tin oxide content of 6.5% by mass or more and less than 16%by mass, is used. The tin oxide content of the target is preferably morethan 8% by mass and less than 16% by mass.

In one embodiment of the manufacturing method of the present invention,a power density of a power source during formation of a transparentelectrode layer is 2.0 W/cm² or more. In another embodiment of themanufacturing method of the present invention, pre-sputtering isperformed at a power density of a power source of 2.0 W/cm² or morebefore the start of formation of a transparent electrode layer. Thepower density of the power source in pre-sputtering is preferably equalto or more than the power density of the power source during formationof the transparent electrode layer. Pre-sputtering may be performedbefore the start of formation of a transparent electrode layer, followedby formation of the transparent electrode layer at a power density of2.0 W/cm² or more.

In the manufacturing method of the present invention, evacuation ispreferably performed until a water partial pressure in a chamber reaches2×10⁻⁴ Pa to 1×10⁻³ Pa before formation of the transparent electrodelayer. The water partial pressure in the chamber during formation of thetransparent electrode layer is preferably 3×10⁻⁴ Pa to 3×10⁻³ Pa.

Further, the present invention relates to a method for manufacturing asubstrate with a transparent electrode in which a low-resistancecrystalline transparent electrode layer is provided on a transparentfilm substrate. By heating the amorphous transparent electrode layer,amorphous ITO is crystallized to obtain a crystalline transparentelectrode layer. A resistivity of the crystalline transparent electrodelayer is preferably 1.5×10⁻⁴ to 3.0×10⁻⁴ Ωcm.

Effects of the Invention

In a substrate with a transparent electrode according to the presentinvention, the tin oxide content of an amorphous transparent electrodelayer is high, and therefore the resistance of the transparent electrodelayer after crystallization is reduced. The density of low-resistancegrains in the amorphous transparent electrode layer is high, andtherefore the time required for completing crystallization of ITO isshort. Further, it is not necessary to excessively reduce the pressurein a chamber before the start of formation of the transparent electrodelayer, and therefore the time required for evacuation is reduced. Thatis, with respect to the substrate with a transparent electrode accordingto the present invention, the resistance can be reduced, and thesubstrate with a transparent electrode according to the presentinvention is excellent in productivity because both the time requireduntil completion of film formation after introduction of a filmsubstrate into a deposition chamber (occupancy time of film depositionapparatus) and the time required for crystallization after completion offilm formation are short, so that the time required for themanufacturing process as a whole can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a substrate with a transparentelectrode according to one embodiment.

FIG. 2 is a schematic view of a substrate with a transparent electrodewhich is provided with parallel electrodes for measuring a change inresistivity during annealing.

FIG. 3 is a view for explaining a method for determining a reaction rateconstant from a graph showing a time-dependent change in resistance ofan ITO film during annealing.

FIG. 4 is a graph showing a time-dependent change in resistance of anITO film during annealing.

FIG. 5 is a graph (Arrhenius plot) in determination of activation energyfor crystallization of an amorphous transparent electrode layer.

FIG. 6 is a view showing a current image (after binarization processing)of a surface of a transparent electrode layer in an Example.

FIG. 7 is a view showing a current image (after binarization processing)of a surface of a transparent electrode layer in a Comparative Example.

MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described below.In each drawing in the present application, dimensional relations ofthickness and so on are appropriately changed for clarification andsimplification of the drawings, and do not reflect actual dimensionalrelations.

FIG. 1 is a schematic sectional view of a substrate 100 with atransparent electrode in which a transparent electrode layer 20 isprovided on a transparent film substrate 10. The transparent electrodelayer 20 is an amorphous film, and contains low-resistance grains 22 inan amorphous phase 21.

[Transparent Film Substrate]

As the transparent film substrate, one that is colorless and transparentin a visible light region is used. As the material of the transparentfilm substrate, for example, it is preferable to use general-purposeresins such as polyester resins such as polyethylene terephthalate(PET), polybutylene terephthalate (PBT), and polyethylene naphthalate(PEN); cycloolefin-based resins; polycarbonate resins; andcellulose-based resins. The glass transition temperature of atransparent film composed of such a general-purpose resin is generallyabout 50° C. to 150° C. A resin such as a transparent polyimide has ahigh glass transition temperature of 200° C. or higher, but a filmcomposed of such an extremely heat-resistant resin is very expensive.Therefore, the material of the transparent film is preferably ageneral-purpose resin as described above in view of reducingmanufacturing costs of the substrate with a transparent electrode. Amongthem, polyethylene terephthalate and the cycloolefin-based resin aresuitably used.

The thickness of the transparent film substrate is not particularlylimited, but is preferably 0.01 to 0.4 mm, more preferably 0.02 to 0.3mm. The film substrate becomes less susceptible to deformation due todeposition as its thickness increases. On the other hand, when thethickness of the film substrate is excessively great, flexibility islost, so that formation of the transparent electrode layer by aroll-to-roll method tends to be difficult. When the thickness of thetransparent film substrate falls within the above-mentioned range,deformation of the film substrate by heat is suppressed, so that atransparent electrode layer can be formed with high productivity by aroll-to-roll method.

As shown in FIG. 1, the transparent film substrate 10 may include anunderlying layer 12 on a transparent film 11. The underlying layer 12serves as a ground for film formation in formation of the transparentelectrode layer 20 on the transparent film substrate 10. For example,when an inorganic insulating layer such as that of silicon oxide (SiOx)is provided as the underlying layer 12, adhesion between the transparentfilm substrate 10 and the transparent electrode layer 20 can beimproved. The transparent film substrate 10 may include an organicmaterial layer or an organic-inorganic composite material layer as theunderlying layer 12. The organic material layer or the organic-inorganiccomposite material layer can act as an easy-adhesion layer or a stressbuffer layer. The underlying layer 12 may include only one layer, or mayhave a laminated structure of two or more layers.

The underlying layer 12 of the transparent film substrate may have afunction as an index-matching layer. For example, by using theunderlying layer 12 in which a medium-refractive-index layer composed ofSiOx (x=1.8 to 2.0), a high-refractive-index layer composed of niobiumoxide and a low-refractive-index layer composed of SiO₂ are laminated inthis order from the transparent film 11 side, the pattern visibilitywhen the transparent electrode layer is patterned can be suppressed. Thestructure of the index-matching layer is not limited to such athree-layer structure. The thickness of each layer can be appropriatelyset while a refractive index, etc., of the material is taken intoconsideration.

When an inorganic insulating layer such as that of silicon oxide orniobium oxide is formed as the underlying layer 12 on the transparentfilm, the method for forming the inorganic insulating layer ispreferably a sputtering method because a homogeneous film having reducedimpurities can be formed, and the film formation speed is high, leadingto excellent productivity. As a sputtering target, a metal, a metaloxide, or a metal carbide can be used.

For the purpose of improving adhesion between the transparent filmsubstrate 10 and the transparent electrode layer 20, a substrate surfacemay be subjected to a surface treatment. Examples of the surfacetreatment method include methods for improving adhesive strength byimparting electrical polarity to a substrate surface. Specific examplesthereof include corona discharge and plasma treatment.

[Transparent Electrode Layer]

The transparent electrode layer 20 composed of ITO is formed on thetransparent film substrate 10. Preferably, the transparent electrodelayer 20 is formed by a sputtering method. The thickness of thetransparent electrode layer is not particularly limited, and isappropriately set according to a desired resistance value, etc. When thesubstrate with a transparent electrode is used for a position detectionelectrode of a touch panel, the thickness of the transparent electrodelayer 20 is preferably 10 nm to 35 nm, more preferably 15 nm to 30 nm.

The ITO transparent electrode layer formed on the transparent filmsubstrate by a sputtering method is an amorphous film in an as-depositedstate immediately after film formation. Preferably, the amorphoustransparent electrode layer 20 contains low-resistance grains 22 in theamorphous phase 21. In this specification, a material having acrystallization rate of 30% or less is defined as being amorphous. Thecrystallization rate is determined from a ratio of an area constitutedby crystal grains in an observation visual field during observation witha microscope.

The tin oxide content of the amorphous transparent electrode layer is6.5% by mass or more and less than 16% by mass based on the total amountof indium oxide and tin oxide. When the tin oxide content falls withinthe above-mentioned range, the resistance of the transparent electrodelayer after crystallization can be reduced. When the tin oxide contentis excessively low, the transparent electrode layer aftercrystallization has a small carrier density, so that sufficientreduction of the resistance cannot be expected. On the other hand, whenthe tin oxide content is excessively high, tin oxide scatters electronsto reduce the mobility, so that the resistance tends to increase.Further, when the tin oxide content is excessively high, the carriercontent in the film may extremely increase to cause absorption of lighthaving a long wavelength, leading to a decrease in transmittance ofvisible light. Thus, to make it possible to perform crystallization in ashorter time, the tin oxide content of the amorphous transparentelectrode layer is preferably 6.5% by mass to 8% by mass. On the otherhand, to further reduce the resistance of the transparent electrodelayer after crystallization, the tin oxide content of the amorphoustransparent electrode layer is preferably more than 8% by mass and lessthan 16% by mass, more preferably more than 8% by mass and 14% by massor less, further preferably 9% by mass to 12% by mass.

In the present invention, the amorphous transparent electrode layer 20preferably has a large number of regions where the current value at avoltage-applied surface is large when a bias voltage is applied thereto.More specifically, when a bias voltage of 0.1 V is applied, the numberof regions where the current value at a voltage-applied surface is 50 nAor more is preferably 50/μm² or more.

A current at the voltage-applied surface is measured in the followingmanner using a scanning probe microscope provided with anelectroconductive cantilever. A measurement region is scanned while acurrent passing into the cantilever is monitored with theelectroconductive cantilever brought into contact with thevoltage-applied surface. By this measurement, a two-dimensionaldistribution of current (current image) is obtained. In thismeasurement, a constant bias voltage is applied to the transparentelectrode layer, and therefore a portion having a large current has alow resistance. In other words, the current image (distribution ofcurrent values) indicates a distribution of resistance.

The obtained current image is subjected to binarization processing witha threshold of 50 nA, a continuous region where the area of a regionwith a current level of 50 nA or more (low-resistance region) is 100 nm²or more is considered as one low-resistance grain, and the number of thelow-resistance grains is counted to determine the number of regionswhere the current value at the voltage-applied surface is 50 nA or more(see FIGS. 6 and 7).

As described above, the amorphous transparent electrode layer 20 beforebeing crystallized (annealed) by heating has low-resistance grains 22buried in the high-resistance amorphous phase 21. By measuring aresistance distribution in a very small region, a distribution oflow-resistance grains can be evaluated. As the density of regions wherethe current value at the voltage-applied surface is large(low-resistance grains) in the amorphous transparent electrode layerincreases, the activation energy required for crystallization tends todecrease, leading to a reduction of the crystallization time. Thedensity of regions where the current level is 50 nA or more ispreferably 50/μm² or more, more preferably 80/μm² or more, furtherpreferably 100/μm² or more, most preferably 120/μm² or more. The upperlimit of the density of low-resistance grains is not particularlylimited. When film formation is performed at a temperature that is nothigher than the heat resistance temperature of the film substrate (150°C. or lower), the density of low-resistance grains in the amorphoustransparent electrode layer is generally 1000/μm² or less, preferably500/μm² or less, more preferably 400/μm² or less.

Preferably, formation of the transparent electrode layer 20 on thetransparent film substrate 10 is performed by a roll-to-roll methodusing a roll-to-roll sputtering apparatus for improving productivity ofthe substrate with a transparent electrode. The power source to be usedfor sputtering deposition is not particularly limited, and a DC, MF, orRF power source or the like is used. For improving productivity of thesubstrate with a transparent electrode, the power source to be used forsputtering deposition of the transparent electrode layer is preferably aDC power source or a MF power source, particularly preferably a DC powersource. Particularly, when pre-sputtering is performed before formationof the transparent electrode layer, the density of low-resistance grainsin the transparent electrode layer can be increased by a short period oftime for pre-sputtering if a DC power source is used.

Preferably, a composite sintered body obtained by solid-dissolving tinoxide with indium oxide is used as a sputtering target. The content oftin oxide in the target is preferably 6.5% by mass or more and less than16% by mass based on the total amount of indium oxide and tin oxide. Thecontent of tin oxide in the target is selected within theabove-mentioned range so that the tin oxide content of the amorphoustransparent electrode layer falls within the above-described range.

The conditions for sputtering deposition of the transparent electrodelayer are not particularly limited as long as the density oflow-resistance grains in an as-deposited state can be made to fallwithin the above-mentioned range. The density of low-resistance grainstends to be increased by performing pre-sputtering before the start offormation of the transparent electrode layer, increasing the powerdensity of the power source during formation of the transparentelectrode layer, raising the substrate temperature, or the like. Morespecifically, an amorphous transparent electrode layer having alow-resistance grain density of 50/μm² or more is formed by performingpre-sputtering at a power density of a power source of 2.0 W/cm² ormore, more preferably 3.0 W/cm² or more, before the start of filmformation; setting the power density of the power source during filmformation to 2.0 W/cm² or more, more preferably 3.0 W/cm² or more;setting the heating temperature (substrate temperature) during filmformation to 100° C. to 150° C., more preferably 100° C. to 120° C.; orcombining these conditions.

It is known that water molecules are adsorbed to a chamber opened to theatmosphere. Water molecules in the chamber are caught in the film duringformation of a transparent conductive oxide layer such as that of ITO,and can act as a factor that hinders crystallization. Thus, when watermolecules are caught in the film, the time for crystallization of theamorphous transparent electrode layer tends to increase. Accordingly, inthe present invention, it is preferable that after the film substrate isput in a sputtering deposition apparatus and before the transparentelectrode layer is formed, the chamber is evacuated to reduce the waterpartial pressure in the chamber. By performing evacuation whileconveying the film substrate, not only water adsorbed to the chamber butalso moisture existing inside and on the surface of the film substratecan be removed, so that the time for crystallization of the amorphoustransparent electrode layer can be reduced.

By evacuation before the start of film formation, the water partialpressure in the chamber is reduced to preferably 1×10⁻³ Pa or less, morepreferably 8×10⁻⁴ Pa or less, further preferably 6×10⁻⁴ Pa or less. Thecrystallization time tends to be reduced as the water partial pressurebefore the start of film formation becomes lower. On the other hand, thetime required for evacuation exponentially increases as the ultimatepressure decreases, and therefore when the water partial pressure beforethe start of film formation is set to be excessively low, the timerequired for a pre-step of film formation (until the start of filmformation after introduction of the film substrate into the chamber)increases, so that productivity may be reduced. Therefore, the waterpartial pressure in the chamber as achieved by evacuation before thestart of film formation is preferably 2×10⁻⁴ Pa or more. The waterpartial pressure in the chamber before the start of film formation andduring film formation can be measured by quadrupole mass spectrometry(Qmass).

When pre-sputtering is performed before the start of formation of thetransparent electrode layer, it is preferable that evacuation isperformed so as to ensure that the water partial pressure in the chamberfalls within the above-mentioned range before pre-sputtering. When aninorganic insulating layer, such as that of silicon oxide, as theunderlying layer 12 and the transparent electrode layer 20 arecontinuously formed using a sputtering deposition apparatus including aplurality of chambers, it is preferable that evacuation is performed soas to ensure that the water partial pressure in the chamber falls withinthe above-mentioned range before the start of formation of the inorganicinsulating layer.

In the present invention, by performing pre-sputtering as describedabove, or adjusting the power density and the substrate temperatureduring film formation, the low-resistance grain density of the amorphoustransparent electrode can be increased to reduce the crystallizationtime without the necessity to excessively decrease the water partialpressure before the start of film formation. “Pre-sputtering” hereinmeans that a part, which does not form a product, of the transparentfilm substrate is subjected to sputtering discharge before the ITOtransparent electrode layer is formed. For example, when the underlyinglayer 12 such as silicon oxide is formed on the transparent film 11,“pre-sputtering” means that discharge is performed after formation ofthe underlying layer and before formation of the ITO transparentelectrode layer.

When pre-sputtering is performed before the start of formation of thetransparent electrode layer, the pressure in the chamber is preferablyequal to or lower than the pressure during formation of the transparentelectrode layer in view of removing impurities on the target byevacuation. The optimum value of the introduction amount of oxygenduring pre-sputtering varies depending on an oxidation state of thesurface of the target, etc. Therefore, it is preferable that dependingon properties of the target, etc., the oxygen partial pressure is set sothat the crystallization time after formation of the transparentelectrode layer is shortened.

The optimum value of the power density during pre-sputtering maysomewhat vary depending on an apparatus size (chamber volume), etc., butis preferably 2.0 W/cm² or more, more preferably 3.0 W/cm² or more asdescribed above. The power density of the power source duringpre-sputtering is preferably equal to or more than the power density ofthe power source during formation of the transparent electrode layer.The power density during pre-sputtering is preferably 1 to 10 times,more preferably 1.5 to 5 times, further preferably 2 to 4 times as largeas the power density during formation of the transparent electrodelayer. When pre-sputtering is performed at a high power density, and thetransparent electrode layer is formed at a power density equal to orlower than the power density for pre-sputtering, the density oflow-resistance grains can be increased while damage to the filmsubstrate, etc., due to deposition is suppressed. Thus, an amorphoustransparent electrode layer which is crystallized in a short period oftime and has a low resistivity after crystallization is obtained.

The temperature during pre-sputtering is not particularly limited, butgenerally ranges from room temperature (about 20° C.) to 150° C.Pre-sputtering may be performed at a temperature lower than roomtemperature (for example, while a film formation roll is cooled). Thepre-sputtering time can be appropriately set according to conditionssuch as a state of the surface of the target, a temperature inpre-sputtering and a power density, but is preferably 3 minutes or more,more preferably 5 minutes or more.

After pre-sputtering is performed as necessary, the transparentelectrode layer is formed while an inert gas, such as argon, and oxygenare introduced into the chamber. The deposition pressure afterintroduction of process gases is preferably 0.2 Pa to 0.6 Pa. Theintroduction amount of process gases such as argon and oxygen duringformation of the transparent electrode layer is set in view of a balancewith a chamber volume, a deposition pressure, a deposition powerdensity, and so on. The introduction amount of an inert gas such asargon is preferably 200 sccm to 1000 sccm, more preferably 250 sccm to500 sccm. The introduction amount of the oxygen gas is preferably 1 sccmto 10 sccm, more preferably 2 sccm to 5 sccm.

The water partial pressure in the chamber during formation of thetransparent electrode layer is preferably 3×10⁻³ Pa or less, morepreferably 2×10⁻³ Pa or less. The crystallization time tends to bereduced as the water partial pressure during film formation becomeslower. On the other hand, to decrease the water partial pressure duringfilm formation, the water partial pressure before the start of filmformation should be decreased, so that the time required for evacuationtends to increase. When attempting to keep the water partial pressureduring film formation low, it may be difficult to increase the size ofthe apparatus, and the types of film substrates that can be used may belimited (use of a film having a large moisture content may bedifficult). Thus, the water partial pressure during film formation ispreferably 3×10⁻⁴ Pa or more, more preferably 5×10⁻⁴ Pa or more.

When pre-sputtering is performed before formation of the transparentelectrode layer, the power density during film formation is notparticularly limited as long as sputtering discharge can be generated,and the power density may be set to any value equal to or more than, forexample, 0.4 W/cm². When pre-sputtering is not performed beforeformation of the transparent electrode layer, the power density information of the transparent electrode layer is preferably 2 W/cm² ormore, more preferably 2.5 W/cm² or more.

On the other hand, the deposition power density is preferably 10 W/cm²or less in view of suppressing film formation damage. When the powerdensity is excessively high, the crystallization speed increases, butthe resistivity after crystallization may not be sufficiently low due todeposition damage, etc. When pre-sputtering is performed before filmformation as described above, the power density during film formationmay be less than 2 W/cm². For example, even when the power densityduring film formation is about 0.4 W/cm² to 0.8 W/cm², an amorphoustransparent electrode layer which has a high density of low-resistancegrains and is crystallized in a short period of time is obtained.

As the substrate temperature during formation of the transparentelectrode layer rises, the density of low-resistance grains tends toincrease, leading to a reduction of the crystallization time. Thus, thesubstrate temperature is preferably 20° C. or higher, more preferably30° C. or higher. The substrate temperature is the temperature of thefilm substrate during film formation. When pre-sputtering is performedbefore formation of the transparent electrode layer, or the depositionpower density is 2 W/cm² or more, the density of low-resistance grainscan be ensured to be 50/μm² or more even in film formation at roomtemperature where heating is not performed during film formation. Evenin film formation at room temperature, the substrate temperature mayrise to about 50° C. because the film formation roll and the filmsubstrate are heated by sputtering discharge. By increasing the powerdensity during pre-sputtering, or increasing the pre-sputtering time,the density of low-resistance grains can be ensured to be 50/μm² or moreeven when film formation is performed at a substrate temperature lowerthan 20° C.

When the substrate temperature during formation of the transparentelectrode layer is 100° C. or higher, the density of low-resistancegrains tends to further increase, leading to a further reduction of thecrystallization time. On the other hand, in view of suppressing damagessuch as thermal deformation of the film substrate, the substratetemperature during formation of the transparent electrode layer ispreferably 100° C. or lower, more preferably 90° C. or lower. In thepresent invention, by performing pre-sputtering, or increasing thedeposition power density, a transparent electrode layer capable of beingcrystallized in a short period of time can be formed without thenecessity to excessively raise the substrate temperature as describedabove.

As described above, the amorphous transparent electrode layer is formedon the transparent film substrate by sputtering to obtain a substratewith a transparent electrode. In the present invention, a transparentelectrode layer capable of being crystallized in a short period of timeis formed without the necessity to perform excessive evacuation andheating at a high temperature. Thus, the process window of filmformation conditions is wide and variations in characteristics withinthe film formation surface are suppressed, so that a large-areasubstrate with a transparent electrode is obtained.

The resistivity of the amorphous transparent electrode layer ispreferably in a range of about 5×10⁻⁴ Ω·cm to 9×10⁻⁴ Ω·cm, morepreferably 6×10⁻⁴ Ω·cm to 8×10⁻⁴ Ω·cm. The carrier density of theamorphous transparent electrode layer is preferably about 3×10⁻²⁰/cm³ to5×10⁻²⁰/cm³. The carrier density in the film tends to increase as thetin oxide content in the ITO film becomes higher.

[Crystallization of Transparent Electrode Layer]

Preferably, the substrate with a transparent electrode according to thepresent invention in which an amorphous transparent electrode layer isprovided on a transparent film substrate has a reduced resistance due tocrystallization of the transparent electrode layer. The amorphoustransparent electrode layer in an as-deposited state is mostly composedof amorphous ITO. When the amorphous ITO is changed into a crystallinestate, the transparent electrode layer has a reduced resistance. Forexample, by heating/annealing the substrate with a transparent electrodein the presence of oxygen, the amorphous transparent electrode layer istransformed into a crystalline transparent electrode layer. The“heating/annealing” described above means a treatment in which heat froma heat source is actively applied to the transparent electrode for acertain period of time for heating during crystallization of ITO,formation of the electrode, or the like. In view of the heat resistanceof the film substrate, the heating/annealing temperature forcrystallization is preferably 180° C. or lower, more preferably 160° C.or lower.

As described above, in the substrate with a transparent electrodeaccording to the present invention, the density of low-resistance grainsin the amorphous transparent electrode layer is high, and therefore thetime required for crystallization is short. Specifically, whenheating/annealing is performed at 150° C., the time required untilcompletion of crystallization is preferably 30 minutes or less. In thepresent invention, the time required to complete crystallization of theamorphous transparent electrode layer can also be reduced to 20 minutesor less, 15 minutes or less, 10 minutes or less, or 5 minutes or less byadjusting film formation conditions, etc. Whether or not crystallizationhas been completed is evaluated from a change in the resistance valuebefore and after immersion of the substrate with a transparent electrodein 7% hydrochloric acid at room temperature for 30 seconds. When theratio of the resistance after immersion to the resistance beforeimmersion is 1.3 or less, it is considered that crystallization has beencompleted. When an acid treatment is performed under the above-mentionedconditions, the amorphous ITO is completely dissolved and removed, andtherefore if crystallization is not sufficient, undissolved crystallineparts remain in the form of islands to be electrically insulated, sothat the resistance considerably increases.

The level of the crystallization speed can also be determined from thecrystallization time as described above, but more strictly, it isevaluated from the activation energy required for crystallization. Inthe substrate with a transparent electrode according to the presentinvention, the activation energy for crystallization of the amorphoustransparent electrode layer is preferably 1.3 eV or less, morepreferably 1.1 eV or less, further preferably 1.0 eV or less. Theactivation energy tends to decrease as the density of low-resistancegrains in the amorphous transparent electrode layer becomes higher. Thecrystallization time becomes shorter as the activation energy decreases.

To calculate the activation energy required for crystallization, theArrhenius equation is used as a relational expression between a rateconstant and a temperature: k=A×exp(−E/RT). k is a rate constant, E isthe activation energy, A is a constant, R is the gas constant, and T isan absolute temperature.

When both sides of the equation are logarithmically transformed andarranged, the equation can be converted into the form ofln(1/k)=−E×1/(RT)−ln(A), and by plotting ln(1/k) on the ordinate andplotting 1/(RT) on the abscissa, the activation energy E can bedetermined from the slope of the straight line (Arrhenius plot). Here,ln denotes a natural logarithm. In the present application, the reactionrate constant k is determined at three temperatures: 130° C., 140° C.,and 150° C., and Arrhenius plotting is performed to calculate theactivation energy E.

The reaction rate constant k can be determined from the relationship ofx=exp(−kt) in the reaction rate theory where x is a reaction rate and tis an elapsed time after the start of reaction. Here, in the process ofcrystallization of the transparent electrode layer, the resistance isreduced with crystallization, and when crystallization is completed, atime-dependent change in resistance is terminated. That is, the amountof change in resistance reflects an amount of change from an amorphousstate to a crystalline state, and by examining a time-dependent changein resistance during heating/annealing, a time-dependent change in thecrystallization process can be examined. Thus, the reaction rateconstant k is determined by monitoring the amount of change inresistance instead of the reaction rate (crystallization rate) x. Thecrystallization rate before heating/annealing is assumed to be 0%, thecrystallization rate after completion of crystallization is assumed tobe 100%, the crystallization rate at the time when the resistancereaches an average value Rh of a resistance value R0 before annealingand a resistance value R_(c) after annealing is assumed to be 50%, thetime th until the resistance reaches the average value R_(h) isdetermined, and x=0.5 and t=t_(h) are substituted in x=exp(−kt) tocalculate the reaction rate constant k.

As described above, in the present invention, an amorphous transparentelectrode layer having a high density of low-resistance grains is formedon the transparent film substrate, and thus rapid crystallization ispossible even when the tin oxide content in the film is higher than 8%by mass. Since the tin oxide content in the film is high, the carrierdensity in the film is high, so that the transparent electrode layerafter crystallization has a reduced resistance. That is, according tothe present invention, a low-resistance substrate with a transparentelectrode can be obtained with high productivity. In the presentinvention, a transparent electrode layer capable of being crystallizedin a short period of time is obtained even when the water partialpressure before film formation is 2×10⁻⁴ Pa or more. Thus, totalproductivity in the process ranging from film formation to heating andcrystallization of the ITO is improved.

Further, in the substrate with a transparent electrode, which isobtained according to the present invention, the resistivity of thetransparent electrode layer after crystallization is preferably 3.0×10⁻⁴Ωcm or less, more preferably 2.7×10⁻⁴ Ωcm or less, further preferably2.5×10⁻⁴ Ωcm or less.

The substrate with a transparent electrode according to the presentinvention can be used as a transparent electrode for a display, alight-emitting device, a photoelectric conversion device, and the like,and is suitably used as a transparent electrode for a touch panel.Particularly, the substrate with a transparent electrode according tothe present invention is suitably used for a capacitive touch panelbecause the transparent electrode layer after crystallization has a lowresistance.

EXAMPLES

The present invention will be described more specifically below byproviding Examples, but the present invention is not limited to theseExamples.

[Measurement of Resistivity]

The sheet resistance of the transparent electrode layer was measured byfour-point probe pressure contact measurement using a low resistivitymeter Loresta GP (MCP-T710 manufactured by Mitsubishi ChemicalCorporation). The resistivity of the transparent electrode layer wascalculated from a product of the value of the sheet resistance and thethickness of the transparent electrode layer. The resistivity aftercrystallization was measured after a sample which had completedcrystallization was taken out from an oven, and cooled to roomtemperature.

[Measurement of Crystallization Time]

As shown in FIG. 2, parallel electrodes were mounted on two oppositeedges of a surface of a substrate 100 with a transparent electrodebefore annealing, on a transparent electrode layer 20 side, and aresistance during annealing was measured. At the time of mounting theparallel electrodes, a distance D between electrodes and a length L ofthe edges on which the electrodes were mounted were made equal to eachother, so that a sheet resistance could be calculated from a resistancevalue. The time until a difference between the resistance value and aresistance value R_(c) at the time when a time-dependent change inresistance was lost was 2 Ω/sq or less was defined as crystallizationcompletion time t_(c). For example, in FIG. 4 (Example 1, heatingtemperature: 150° C.), it is apparent that the resistance value R_(c) atthe time when the time-dependent change in resistance is lost is 100Ω/sq, and the crystallization completion time t_(c) is 15 minutes.

[Measurement of Activation Energy]

The activation energy E at the time of crystallizing the amorphoustransparent electrode layer was calculated from a dependency of areaction rate constant k on temperature at the time of heating/annealingthe substrate with an amorphous transparent electrode layer at apredetermined temperature to be crystallized. For each heatingtemperature, the heating time was plotted on the abscissa axis and thesurface resistance of the transparent electrode layer was plotted on theordinate axis, and a time t was determined at which the surfaceresistance value reached an average of the initial value (at the startof measurement) and the final value (state in which crystallization wascompleted to achieve a crystallinity degree of almost 100%). A reactionrate constant k was calculated at each heating temperature bysubstituting a reaction ratio of 0.5 into the equation: reactionratio=1−exp(kt) with the reaction ratio considered to be 50% at the timet.

From the reaction rate constant k and heating temperature at each ofheating temperatures of 130° C., 140° C. and 150° C., Arrhenius plotting(abscissa axis: 1/RT and ordinate axis: ln(1/k)) was performed, and theslope of the line was defined as an activation energy E. An Arrheniusplot in Example 1 is shown in FIG. 5. From the slope of the graph inFIG. 5, the activation energy for crystallization: E=1.25 eV wasdetermined.

[Measurement of Low-Resistance Grains]

For measurement of the number of low-resistance regions, current imagemeasurement was performed using an electroconductive cantilever(SI-DF3R, manufactured by SII NanoTechnology Inc., spring constant: 1.6N/m) with a contact surface coated with rhodium at a thickness of 30 nmin a scanning probe microscope system (NanoNaviReal, manufactured by SIINanoTechnology Inc., scanner model: FS 20N) provided with a scanningprobe microscope unit (Nanocute) and a measurement control unit(NanoNavi Probe station), and low-resistance regions were evaluated froma current image distribution.

A substrate with a transparent electrode was cut to a 5 mm square, andan ITO film surface and a sample holder were brought into conductionwith each other with a copper tape interposed therebetween. A probe wasbrought into contact with a sample, a bias voltage of 1 V was thenapplied from the holder, and the sample was scanned over a range of 2μm² to eliminate static electricity. The applied voltage was thenchanged to 0.1 V while keeping the probe in contact with the sample, thesample was scanned over a range of 1 μm² in the vicinity of the centerof the region where static electricity was eliminated, and a shape imageand a current image were obtained by two-screen measurement. Themeasurement was performed in an environment at room temperature.Detailed measurement conditions are as follows.

Measurement mode: AFM

Deflection amount: −1 mm

Scanning frequency: 1.08 Hz

I gain: 0.45

P gain: 0.11

A gain: 0

DIF sensitivity: 40.00 mV/nm

Dissolution (X×Y): 256×256

Image quality: standard

The current image was subjected to binarization processing with acurrent value of 50 nA as a threshold using an analysis program(NanoNaviStation ver 6.00B) attached to the device. Here, tiltcorrection was not performed. FIG. 6 shows the current image of Example1 subjected to binarization processing. In the current image subjectedto binarization processing, a continuous region where the area of a partwith a current value of 50 nA or more (white part in FIG. 6) was 100 nm²or more was considered as one low-resistance grain, and the number ofthe low-resistance grains was counted. From FIG. 6, the number oflow-resistance grains can be found to be 51/μm².

[Measurement of Crystallization Rate]

The total amount of crystal components contained in the transparentelectrode layer before performing annealing was evaluated by fullyetching away amorphous components, and calculating the area of remainingcrystal grains. As an etching condition, the sample was immersed in 1.7%hydrochloric acid at room temperature for 90 seconds, and then washedwith flowing water. The surface of the sample was photographed by ascanning electron microscope, and the amount of remaining crystalcomponents was determined from the image.

Example 1

Using a roll-to-roll-type sputtering apparatus, a silicon oxide layerand a transparent electrode layer were formed on a PET film substratewith a hard coat layer formed on each of both surfaces thereof, the PETfilm substrate having a glass transition temperature of 80° C.

First, the film substrate was introduced into a film depositionapparatus, evacuation was performed until the water partial pressure ina chamber reached 4×10⁻⁴ Pa while the film was conveyed in the filmdeposition apparatus. Evacuation required 2 hours.

After the chamber was evacuated, a silicon oxide layer was formed byperforming sputtering at a power density of 3.0 W/cm² using a MF powersource under the conditions of a substrate temperature of 40° C. and achamber pressure of 0.2 Pa while supplying oxygen at a flow rate of 20sccm and argon at a flow rate of 100 sccm with the use of Si as atarget. The obtained silicon oxide layer had a thickness of 45 nm.

Pre-sputtering was performed at a power density of 3.0 W/cm² for 15minutes using a DC power source under the conditions of a substratetemperature of 40° C., a chamber pressure of 0.3 Pa and a water partialpressure of 1×10⁻³ Pa while oxygen at a flow rate of 4.0 sccm and argonat a flow rate of 250 sccm were supplied into the chamber with the useof a composite oxide sintered target (tin oxide content: 10% by mass) ofindium oxide and tin oxide. After pre-sputtering, the oxygen flow ratewas changed to 2.0 sccm, and sputtering deposition was performed at apower density of 0.6 W/cm² using the DC power source, thereby forming anITO transparent electrode layer on the silicon oxide layer. The obtainedtransparent electrode layer had a thickness of 26 nm.

The oxygen flow rate during formation of the transparent electrode layerwas set so as to minimize time required for crystallization whenconditions other than the oxygen flow rate were the same (the sameapplies for Examples and Comparative Examples below). The substratetemperature during film formation was determined by attaching a thermolabel (TEMP-PLATE manufactured by I.P. LABOLATORIES, INC) to thetransparent film substrate beforehand, and reading a maximum temperatureof the thermo label after completion of film formation. A region thatwould not be heated in evacuation was selected, and the thermo label wasattached to the region. The thickness of the transparent electrode layerwas determined by observation of a cross section with a transmissionelectron microscope (TEM). The water partial pressure before the startof film formation and during film formation was measured usingquadrupole mass spectrometer.

Example 2

Pre-sputtering was not performed before formation of a transparentelectrode layer, and the oxygen flow rate was 4.0 sccm and the powerdensity was 3.0 W/cm² during formation of the transparent electrodelayer. A substrate with a transparent electrode was prepared in the samemanner as in Example 1 except that the above-mentioned changes weremade. The obtained transparent electrode layer had a thickness of 26 nm.

Example 3

Pre-sputtering was performed for 15 minutes before formation of atransparent electrode layer, and an ITO transparent electrode layer wasthen formed under the same conditions as in the pre-sputtering. Asubstrate with a transparent electrode was prepared in the same manneras in Example 1 except that the above-mentioned changes were made. Theobtained transparent electrode layer had a thickness of 26 nm.

Example 4

The degassing temperature before film formation and the substratetemperature during film formation were 120° C. A substrate with atransparent electrode was prepared in the same manner as in Example 3except that the above-mentioned changes were made. The obtainedtransparent electrode layer had a thickness of 26 nm.

Example 5

The degassing temperature before film formation and the substratetemperature during film formation were 120° C. A substrate with atransparent electrode was prepared in the same manner as in Example 1except that the above-mentioned changes were made. The obtainedtransparent electrode layer had a thickness of 26 nm.

Comparative Example 1

A substrate with a transparent electrode was prepared in the same manneras in Example 1 except that pre-sputtering was not performed beforeformation of the transparent electrode layer. The obtained transparentelectrode layer had a thickness of 26 nm.

Comparative Example 2

A substrate with a transparent electrode was prepared in the same manneras in Example 5 except that pre-sputtering was not performed beforeformation of the transparent electrode layer. The obtained transparentelectrode layer had a thickness of 26 nm.

Comparative Example 3

Before film formation, evacuation was performed until the water partialpressure in a chamber reached 1×10⁻⁴ Pa. The water partial pressureduring formation of a transparent electrode layer decreased to 2×10⁻⁴Pa. A substrate with a transparent electrode was prepared in the samemanner as in Comparative Example 2 except that the above-mentionedchanges were made. The obtained transparent electrode layer had athickness of 26 nm. However, in Comparative Example 3, the time requiredfor reducing the water partial pressure in the chamber to 1×10⁻⁴ Pabefore film formation was 30 hours. In Comparative Example 3,heating/annealing was performed at 150° C. after formation of theamorphous transparent electrode layer, but crystallization was notcompleted 30 minutes after the start of heating, and the resistivity was4.4×10⁻⁴ Ω·cm.

Conditions for formation of the transparent electrode layer,characteristics of the amorphous film after film formation,crystallization conditions (crystallization time and activation energy),and characteristics after crystallization in the Examples andComparative Examples described above are shown in Table 1.

TABLE 1 Compar- Compar- Compar- Exam- Exam- Exam- Exam- Exam- ativeative ative ple 1 ple 2 ple 3 ple 4 ple 5 Example 1 Example 2 Example 3Steps before Degassing Temperature (° C.) 90 90 90 120 120 90 120 120film Water partial pressure 4 4 4 4 4 4 4 1 formation (×10⁻⁴ Pa)Pre-sputtering Power density (W/cm²) 3 — 3 3 3 — — — Time (minutes) 1515 15 15 Film Power density (W/cm²) 0.6 3 3 3 0.6 0.6 0.6 0.6 formationTemperature (° C.) 40 40 40 120 120 40 120 120 conditions Pressure (Pa)0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Film formation Ar (sccm) 250 250 250 250250 250 250 250 gas flow rate O₂ (sccm) 2 4 4 4 2 2 2 2 Water partialpressure (×10⁻⁴ Pa) 10 10 10 10 10 10 10 2 Character- Density oflow-resistance grains (/μm²) 51 62 101 188 138 8 27 25 istics ofCrystallization rate 2.9% 4.6% 5.2% 18.0% 5.8% 1.3% 5.1% N.D. amorphousfilm Resistivity (×10⁻⁴) Ω · cm) 7.4 7.2 7.2 6.1 6.5 7.4 6.4 6.8Crystallization Crystallization completion time (minutes) 15 15 5 3 152400 120 60 Activation energy (eV) 1.25 1.14 0.79 0.48 1.2 1.57 1.461.37 Characteristics Resistivity (×10⁻⁴ Ω · cm) 2.2 2.4 2.5 2.6 2.3 3.22.3 2.3 after crystallization

The results in Table 1 show that annealing time required forcrystallization depends on a density of low-resistance grains, and thusthe time for crystallization can be reduced as the number oflow-resistance grains in the amorphous film increases. Specifically,when the density of low-resistance grains is 50/μm² or more,crystallization is completed in 30 minutes or less. The activationenergy required for crystallization here is 1.3 eV or less. That is,when the amorphous transparent electrode layer in an as-deposited stateafter film formation contains a large number of low-resistance grains,the activation energy E for crystallization is low, and rapidcrystallization is possible.

Comparison of Example 1 and Comparative Example 1 shows that whenpre-sputtering is performed before deposition of ITO, the number oflow-resistance grains increase, leading to an increase incrystallization speed. Comparison of Example 2 and Comparative Example 1shows that when the transparent electrode layer is formed at a highpower density, an effect comparable to that of pre-sputtering can beobtained. Comparison of Examples 1 and 2 and Example 3 shows that whenpre-sputtering is performed, and the transparent electrode layer is thenformed at a high power density, the crystallization speed furtherincreases.

Comparison of Example 1 and Example 5 and comparison of Example 3 andExample 4 show that when the transparent electrode layer is formed at ahigh substrate temperature, the crystallization speed further increases.On the other hand, comparison of Examples 1 and 2 and ComparativeExample 2 and comparison of Comparative Example 1 and ComparativeExample 2 show that the crystallization speed can be more effectivelyincreased by performing pre-sputtering or performing film formation at ahigh power density rather than performing film formation at a highsubstrate temperature (film formation temperature). Examples 1 to 5 showthat by combination of film formation conditions such as pre-sputteringbefore formation of the transparent electrode layer, increasing of thepower density during film formation, raising of the substratetemperature, and so on, the number of low-resistance grains can beincreased to further reduce the crystallization time.

Comparison of Comparative Example 2 and Comparative Example 3 shows thatwhen the evacuation time before the start of film formation isincreased, the water partial pressure before the start of film formationand during film formation decreases, leading to an increase incrystallization speed. However, in Comparative Example 3, considerabletime is required for evacuation before the start of film formation forreducing the water partial pressure in the chamber. Thus, rather thanthe effect of improving productivity by reduction of the crystallizationtime, reduction of productivity due to an increase in the evacuationtime (occupancy time of film deposition apparatus) before the start offilm formation becomes noticeable, resulting in deterioration ofproductivity.

The density of low-resistance grains in Comparative Example 2 issubstantially comparable to that in Comparative Example 3, and inComparative Example 3, the time required for crystallization is longeras compared to Examples 1 to 5. These results show that reduction of thetime for crystallization of the transparent electrode layer according tothe present invention is based on a mechanism different from that ofreduction of the crystallization time by reduction of the water partialpressure as has been known previously, and the present invention issuperior to conventional techniques in both improvement of productivityand resistance reduction.

Example 6

Using a roll-to-roll-type sputtering apparatus, a silicon oxide layerand a transparent electrode layer were formed on a PET film substratewith a hard coat layer formed on each of both surfaces thereof, the PETfilm substrate having a glass transition temperature of 80° C.

First, the film substrate was introduced into a film depositionapparatus, evacuation was performed until the water partial pressure ina chamber reached 2×10⁻⁴ Pa while the film was conveyed in the filmdeposition apparatus. After the chamber was evacuated, a silicon oxidelayer having a thickness of 3 nm was formed under the same conditions asin Example 1.

Pre-sputtering was performed at a power density of 5.0 W/cm² for 180minutes using a MF power source under the conditions of a film formationroll temperature (set temperature) of −20° C., a chamber pressure of 0.2Pa and a water partial pressure of 1×10⁻³ Pa while oxygen at a flow rateof 1.2 sccm and argon at a flow rate of 400 sccm were supplied into thechamber with the use of a composite oxide sintered target (tin oxidecontent: 7.5% by mass) of indium oxide and tin oxide. Afterpre-sputtering, an ITO transparent electrode layer was formed on thesilicon oxide layer by performing sputtering deposition under the sameconditions as those for the pre-sputtering. The thickness of theobtained transparent electrode layer was 26 nm, the resistivity was6.0×10⁻⁴ Ω·cm, and the number of low-resistance grains per 1 μm² was 56.

The transparent electrode layer was heated at 150° C. to becrystallized. The time required to complete crystallization was 20minutes, and the resistivity of the transparent electrode layer aftercrystallization was 2.2×10⁻⁴ Ω·cm. The activation energy forcrystallization was 1.27 eV.

The results from Example 6 show that even when the tin oxide content is8% by mass or less, an amorphous transparent electrode layer with thenumber of low-resistance grains being 50/μm² or more can be formed, andthe transparent electrode layer can be crystallized in a short period oftime of 30 minutes or less.

The invention claimed is:
 1. A substrate with a transparent electrode,comprising: a transparent film substrate; and a transparent electrodelayer on the transparent film substrate, wherein the transparentelectrode layer has a crystallization ratio of 30% or less, thetransparent electrode layer comprises an amorphous indium-tin compositeoxide having a tin oxide content of 6.5% by mass to 8% by mass, and thetransparent electrode layer includes low-resistance grains with adensity of 50/μm² or more, wherein each of the low-resistance grains isa continuous region having an area of 100 nm² or more where a currentvalue at a voltage-applied surface is 50 nA or more when a bias voltageof 0.1V is applied to the transparent electrode layer.
 2. The substratewith the transparent electrode according to claim 1, wherein timerequired for crystallization of the transparent electrode layer is 30minutes or less when the transparent electrode layer is heated at 150°C.
 3. The substrate with the transparent electrode according to claim 1,wherein activation energy for crystallization of the transparentelectrode layer is 1.3 eV or less.
 4. The substrate with the transparentelectrode according to claim 1, wherein a resistivity after thetransparent electrode layer is subjected to a heating treatment at 150°C. for 30 minutes is 1.5×10⁻⁴ to 3.0×10⁻⁴ Ωcm.
 5. The substrate with thetransparent electrode according to claim 1, wherein the transparentelectrode layer has a thickness of 10 nm to 35 nm.